Irma developed on August 30, 2017 near the
Cape Verde Islands, from a
tropical wave that had moved off the west African coast three days prior.[1][2][3] Under favorable conditions, Irma
rapidly intensified shortly after formation, becoming a Category 2 hurricane on the
Saffir–Simpson scale within a mere 24 hours. It became a
Category 3 hurricane (and therefore a major hurricane) shortly afterward; however, the intensity fluctuated between Categories 2 and 3 for the next several days due to a series of
eyewall replacement cycles. On September 4, Irma resumed intensifying, becoming a Category 5 hurricane by early the next day. On September 6, Irma reached its peak intensity with 185 mph (295 km/h) winds and a minimum
pressure of 914 hPa (27.0 inHg), making it the second most intense tropical cyclone worldwide so far in 2017, behind only
Hurricane Maria, and the strongest worldwide in 2017 in terms of wind speed. Another eyewall replacement cycle caused Irma to weaken back to a Category 4 hurricane, but the storm attained Category 5 status for a second time while making landfall in Cuba. After dropping to Category 3 intensity due to land interaction, the storm re-intensified to Category 4 status as it crossed warm waters between Cuba and Florida, before making landfall on
Cudjoe Key with maximum sustained winds at 130 mph (215 km/h). Irma dropped back to Category 3 by the time it made a second Florida landfall on
Marco Island. Irma weakened to a Category 2 hurricane later that day, the first time it weakened below major hurricane status in over a week, and eventually dissipated off the coast of
New England.

Meteorological history

The
National Hurricane Center (NHC) began monitoring a
tropical wave over western Africa on August 26.[10] This wave moved off the coast of the continent late on August 27. Throughout the next two days, showers and thunderstorms associated with the wave became better organized and gradually coalesced into a
low pressure area, as the system passed just south of and then through the
Cape Verde Islands on August 29,[11] with the NHC stating that any significant organization of the disturbance would result in the classification of a tropical depression.[12] Further organization over the next 24 hours or so led to classification of the disturbance as Tropical Storm Irma, at 15:00 UTC on August 30, based on
scatterometer data and
satellite estimates.[13] With warm
sea surface temperatures and low wind shear, strengthening was anticipated, with the only hindrance being slightly cooler waters and drier air.

The nascent storm began developing upper-level poleward
outflow as an
anticyclone became established over the system, with
banding features becoming increasingly evident in satellite images.[14] Early on August 31, shortly after the development of a
central dense overcast (CDO) and an
eye feature, Irma
rapidly intensified beginning at 09:00 UTC on August 31, with winds increasing from 70 mph (110 km/h) to 115 mph (185 km/h) in only 12 hours.[15] On September 2, a ship passed 60 mi (90 km) to the west of the center of Irma, recording maximum winds of 45 mph (70 km/h), which indicated that the eye of Irma remained compact.[16][17] A strengthening subtropical ridge over the central North Atlantic pushed Irma from a western to southwestern direction on September 2 and 3.[18][19][20][21] The first
aircraft reconnaissance mission departed from
Barbados on the afternoon of September 3, discovering an eye 29 mi (47 km) in diameter and surface winds of 115 mph (185 km/h).[20][22]

Infrared loop of Hurricane Irma approaching the northern Leeward Islands on September 5, around the time of its upgrade to a Category 5 hurricane

Satellite image of Irma's extratropical remnant over the Eastern United States, on September 13.

On September 4, after moving into more favorable conditions, Irma strengthened into a Category 4 hurricane.[23] As it continued approaching the Leeward Islands, Irma underwent a second and more robust period of rapid intensification, becoming a Category 5 hurricane by 11:45 UTC on the following day, with winds of 175 mph (280 km/h).[24] As it began to take on
annular characteristics, the extremely powerful hurricane continued to intensify,[25] with maximum sustained winds peaking at 185 mph (295 km/h) near 00:00 UTC on September 6 – which would remain steady and unchanged for the next 37 hours. Six hours later, Irma made landfall along the northern coast of
Barbuda near peak strength.[26] Later that day, around 21:00 UTC, the storm's pressure bottomed out at 914 hPa (27.0 inHg) – this was the lowest in the Atlantic since
Dean in 2007. While maintaining its intensity, Irma made successive landfalls at approximately 12:00 UTC on
Sint Maarten, and at 17:00 UTC on
Ginger Island and
Tortola, in the
British Virgin Islands.

Sea surface temperatures in Hurricane Irma's path.

Shortly before 06:00 UTC on September 8, Irma made landfall on the Bahamian island
Little Inagua.[27] About three hours later, Irma weakened into a Category 4 hurricane but regained Category 5 status 18 hours later before losing it again over Cuba. At 13:10 UTC on September 10, Irma made landfall in
Cudjoe Key, Florida with maximum sustained winds of 130 mph (215 km/h) and a central pressure of 929 hPa (27.4 inHg).[28] Later on that day, at 19:35 UTC, Irma made landfall in
Marco Island with maximum sustained winds of 115 mph (185 km/h) and a central pressure of 940 hPa (28 inHg); the Marco Island Police Department recorded a wind gust of 130 mph (215 km/h).[29] The
Naples, FL Municipal Airport measured wind gusts up to 142 mph (229 km/h). About a half an hour later, Irma made landfall in Naples at the same intensity. Irma weakened into a Category 2 storm once inland, and below hurricane intensity at 12:00 UTC on September 11. At 03:00 am UTC on September 12, Irma weakened to a tropical depression over the Georgia-Alabama border, and degenerated into a post-tropical low about 24 hours later north of
Tupelo, Mississippi.[30] Irma's remnants continued moving towards the northwest over the next day, before turning northward and then accelerating to the northeast on September 14.[31] Early on September 15, Irma's remnants began moving off the New England coastline, and became increasingly disorganized, while continuing to weaken. Later on the same day, Irma's remnants began interacting with a cold front stretching over
Newfoundland.[32] On September 16, Irma's remnant circulation collapsed, and the majority of Irma's remnant moisture was absorbed into
Hurricane Jose later in the day.[33]

Data collected by NASA showed ocean surface temperatures in the path of Irma were above 30 °C (86 °F) at the time, more than enough to sustain a
Category 5 hurricane.[34] Additionally, ocean surface temperatures in areas between Cuba and south Florida extended to 32 °C (90 °F),[35][36] which was warm enough to intensify Irma into a much stronger 200 miles per hour (320 km/h) storm, if ideal conditions had been met.[37]